Ok take my words with a grain of salt as I do not know coco that well, I'm starting myself with it and finishing a run in soil. i red a lot of things about coco and talked to people who runs with coco before i decide to switch to this so promising medium.
What I'm going to tell you is what I would do if I were you.
First pics would be welcome, as it could help us see what kind of yellowing you have.
Are you sure about the pH of your water? Take your water, mix it with your nutrients adjust pH if needed, let it rest for an hour, shake it and read the pH. What's the figure?
What are the size of the pots they're in right now?
Does the "Burpee" coco comes hydrated or compressed?
Did you try to take some of the coco and rinse it once or twice and then test the runoff with your RO water? Get back at us with the result.
I mean for what we know, we are not even sure the runoff test is a good way to measure overfertilization. But what's sure is that this yellowing comes from somewhere and we need to find where!
Can you get some pics?
Carl Carlson: I can't open the webpage with the test. Seems like a good info, can you paste it here?
I am a Hydro Grower, this is my first attempt at Coco. I am very anal about pH and EC. pH feeding is 5.5-5.6 and ppm is 600. I checked the Burpee, compressed brick, with just straight RO water. It was 700ppm right out of the bag. This is what is causing the yellowing, I am positive of that. But what do I do, just water using RO water for a few days? Feed half Strength? I need to get the salts out of the Coco, so flushing would be nice...but how often and how much?
I tested the Botonicare Boss coco right out of the bag was 250-300 ppm. I rinsed it a few times and got it down to zero. This is what I will use for my new seedlings and clones. I just need to fix the other cups that have the Burpee coco. They are all in Beer cups for now. No pics yet, but can put some up tomorrow. Anyone else have a suggestion?